1. Field of the Invention
The present invention relates to a method and system for measuring a heart rate of an object, such as a person to be examined, on the basis of a heartbeat signal acquired from the object.
2. Description of the Related Art
In recent years, applications of an electrocardiogram data indicative of the diastolic and systolic actions of the heart have been spread into various fields. Because it has been found that the influence of stress and fatigue caused in the human has come out as fluctuations in a heart rate or heart rate variability, the electrocardiogram data has been used in the field of human engineering and medical industry as well as the field of medical care, such as finding and diagnosis of cardiovascular diseases and monitoring medical conditions. Therefore, it is a recent demand to commercialize compact measurement apparatuses capable of measuring an amount of the heart rate and information in relation to heart rate variability.
As to the conventional measurement of the heart rate, there has been known an electrocardiogram analysis apparatus that is able to compute the heart rate based on a heart rate signal appearing due to excitation at the atrium of the heart. This type of electrocardiogram analysis apparatus is represented by the apparatus disclosed by Japanese Patent-laid Open (KOKAI) publication No. 1995-016214.
In this electrocardiogram analysis apparatus, a heartbeat signal is acquired from a person to be examined so that electrocardiogram (ECG) waveform data showing cyclically repeated movements of the heart can be obtained. This electrocardiogram waveform data is then subjected to detection of an R wave having a maximum peak and appearing every heartbeat in the electrocardiogram (ECG) waveform. Then peak-to-peak intervals (noted as R-R intervals) are detected, and used for calculating the heart rate of the person to be examined.
In detail, the operation for such a measurement carried out by the apparatus disclosed by the above publication is as follows.
First, the continuously acquired heartbeat signal is converted into electrocardiogram waveform data, and one frame of data in the electrocardiogram waveform data is sampled at a predetermined sampling frequency. The one frame of data is then subjected to pattern matching (cross-correlation processing) with previously prepared template data, which is a set of reference waveform data that imitates R waves, so that the R waves can be enhanced. Finally, an R-R interval, of which R waves have been enhanced, is obtained, subjected to computation of a reciprocal thereof, and multiplied by 60, whereby an amount of the heart rate per minute can be obtained.
However, the above conventional electrocardiogram analysis apparatus has suffered from the problem that error in the detection of R waves from the electrocardiogram waveform is obliged to be larger.
By nature, the measurement of the electrocardiogram waveform is affected largely by individual differences. Insufficient noise removal from the heart rate signal will spoil an accurate production of electrocardiogram waveform data.
In particular, the foregoing conventional electrocardiogram analysis apparatus has a poor performance in removing noise from the detected heart rate signal, because the pattern matching carried out in the conventional electrocardiogram analysis apparatus is not necessarily effective. Specifically, in the conventional electrocardiogram analysis apparatus, only wave elements collected from around an R wave (data from a range of 10 msec that covers an R wave), such as P wave and T wave, are pattern-matched with the reference waveform data. However, the electrocardiogram waveform elements, such as PQ interval, QT interval, and T-wave amplitude, have large influence resulting from individual differences, thus being apt to an erroneous detection of the R waves.